Telegraph circuit



April 20, 1937. F s. KI'NKEAD ET AL TELEGRAPH C IRCUIT Filed Aug. 31,1935 4 Sheets-Sheet 1 GL4. LDC/(E licg) ATTORNEY 7 April 1937- F. s.KINKEAD ET AL 2,077,936

TELEGRAPH CIRCUIT Filed Aug. 31, 1935 '4 Sheets-Sheet 2 /N 1/5 N TORS win Qt Tll {A m% April 1937. F. s. KINKEAD El AL 2,077,936

TELEGRAPH CIRCUIT Filed Aug. 31, 1935 4 Sheets-Sheet 3 .FSK/N/(EADGALOCKE ATTORNEY April 20, 1937.

F. s. KINKEAD El AL TELEGRAPH CIRCUIT Filed Aug. 31, 1935 //V l/E N TORSA TTORNE 1 4 Sheets-Sheet 4 F5. KIN/(E140 G.A.LOCKE Patented Apr. 20,1937 UNITED STATES PATENT OFFICE TELEGRAPH CIRCUIT York ApplicationAugust 31, 1935, Serial No. 38,676

18 Claims.

This invention relates to telegraph switching systems and moreparticularly to systems of this type in which telegraph lines can beinterconnected for communication by an attendant at a switching station.The invention also relates to systems of this type in which a pluralityof stations can be interconnected simultaneously for broadcasting orconference purposes.

It is an object of the invention to provide a switching system in whichtelegraph lines or telegraph loops may be interconnected for twowaycommunication. More particularly, it is an object to provide a system inwhich more than two stations or lines can be directly interconnected fortwo-way communication between them.

It is a further object to provide an equipment whereby a plurality ofseparate interconnections may be simultaneously set up to establishtwoway communication within each of a plurality of groups of lines.

It is a further object to provide a system of this type in which a largeplurality of the line circuits or loops may be interconnected forbroadcasting and conference purposes irrespective of whether or notthese lines are already in communication; and it is a specific object toarrange for the restoration of the set-up of the various connectionsafter the broadcasting has ceased.

It is still another object of the invention to arrange the system insuch a manner that the calling lamp and operators key at the switchingsystem may be located at a point remote from the repeater bay and relayrack without the use of an excessive number of control wires.

Other objects of the invention have to do with simplification,efiiciency and low cost in a system of this type.

In a telegraph switching system arranged in accordance with theinvention, each line circuit is permanently terminated at the mainrepeater station in a simple repeater permitting of twowaycommunication; a call relay is associated with the line for control of acall lamp on the attendants switchboard included in a one-wire seriescircuit connected to a plurality of locking keys; the series circuitalso includes a winding of a control relay for cutting through the lineto an interconnecting circuit. Other control or switching relays areassigned to each line circuit for cutting the line through to otherinterconnecting or link circuits depending upon which key is depressedby the operator.

In the preferred form of the system, the twoway repeater associated witheach line is of the interconnecting type in which the local side of therepeater is adapted for operation with a great number of other similarrepeaters for twoway communication. Such a repeater is described inpatent application Serial No. 32,866, filed by Kinkead and Locke on July24, 1935.

When a line calls, the corresponding, call lamp will be lighted withoutthe line being cut through; the attendant presses a key for a linkcircuit which is idle and thereby cuts the line through to thatlink,which normally is connected through a similar interconnecting repeaterto the attendants printer set. Upon exchange of information between theline and the attendant, the attendant presses keys for such other linesas are desired for communication with the calling line and correspondingto the selected link circuit, thereby operating control relays forcutting the lines through to the link circuit.

For broadcasting purposes thev arrangement is such that all the controlor switching relays associated with the first or main link areautomatically operated by a call signal from the broadcasting station tocut all lines through to that link, and simultaneously therewith theswitching relays for all other links, which may have been operated bythe keys, are automatically released, thereby disconnecting theassociated lines from all other link circuits. Upon cessation ofbroadcasting, all the control circuits are automatically restored andinasmuch as the attendants keys have remained in locked position, suchcontrol or switching relays will again be operated as were used insetting up the connections before the broadcast call, so that thoseconnections will be reestablished.

The broadcasting arrangement may be made in different manners. Thus, anyone of the lines may request a broadcast set-up and the attendant, bydepressing a single key, will bring about the necessary switchingoperation and, by restoring the key after the broadcast, reestablish theprevious interconnection. In accordance with another arrangement thebroadcasting may be from a special station, remote from the switchingstation, and equipped with remote control apparatusfor setting up thebroadcast connection to all stations onthe first link and subsequentlyrestore the previous interconnection. For this purpose an automaticswitching device responsive to a predetermined signal code will bringabout the necessary switching opera tions required for'setting up thebroadcast con nection and for restoring the original intercona repeaterand switching station for a state police system and in which Figs. 1 and1A illustrate different repeater and control circuits directlyassociated with the incoming lines;

Fig. 2 shows the special control circuit associated with the line fromheadquarters; and

Fig. 3 shows the attendants equipment for recording of all messagestransmitted over the system.

Throughout the system shown in the drawings, a number of links or hubsH, H-l and H--2 are shown which are one-wire circuits forinterconnection of the various repeaters; any number of theseinterconnecting or link circuits may be provided in accordance with therequirements.

As shown in Fig. 3, each link circuit is connected with a hub repeaterHR, H-|R, H-2R to individual attendants recorder sets AP, AP--l,

AP2, respectively.

As shown in Fig. 2, each link or hub isconnected with one repeater SR,SR-l, SR-2, respectively, over individual lines to recorders BCR at thebroadcasting station or headquarters. In Fig. 2 there is also shown abroadcasting control circuit BCC for receiving signals over the line BLfrom the broadcasting transmitter BCT and for impressing signals on thefirst or main link circuit H. In Fig. 1, the link circuits are shownconnected through a relay control circuit RCC--A and through a repeaterRA to a line circuit LA which is shown as including three stationsconnected in series and located some distance apart. In Fig. 1, the linkcircuits are similarly shown connected to a relay control circuit RCCBto a group of repeaters RB-I, RB2, RB-3, connected in multiple andoperating into the line circuits LBI, LB2, LB-B to outlying stations SB.The line circuit may include different numbersof stations.

In, Fig. 1-A, the link circuits are shown connected through a relaycontrol circuit RCCC through a repeaterRC to a line circuit LC; thearrangement of circuits RCCC and repeater RC are shown to illustrate analternative to the arrangements shown in Fig. 1.

In Fig. 1-A the link circuits are also shown connected through a relaycontrol circuit RCC-D and a repeater RD operating over the line circuitLD into a distant group of repeaters RD-l, RD-2, RD-3, which, in turn,operate into line circuits LD-2 and LD-3, which may have difierentnumbers of stations serially included in them.

The stations SA, SB, SC andSD may be as-, sumed to be scattered over astate and to each include a teletypewriter equipment for reception andtransmission of telegraph messages, operating on the start-stopprinciple as is'well known. Thus, a group of stations such as'SDmaycover a remote section of the state and would be connected throughagroup of repeaters suchas the repeaters RD-2, RD3, and the group willbe connected over a long line circuit to the main repeater station bymeans of repeaters RD--l and RD.

Stations such as SA, SB and SC may be assumed to be located in an areasurrounding the main repeater station; their 'line'circuits thus will beconnected directly to repeaters in the main station.

'The headquarters is, in the present instance, assumed .to be locatedsome distance from the main repeater station and is equipped withrecorders BCR individual to each link circuit in the repeater stationfor recording of all messages in the whole system. -One of theserecorders being associated withthe main or broadcasting link, a homerecord will be made at headquarters 01' messages transmitted fromheadquarters. The transmitting relay BCT shown in Fig. 2 may beoperatedin any desirable manner, such as from a teletypewriter keyboard.

In the particular embodiment described in connection with the drawings,it is assumed that the repeaters and relays of the main station arelocated, for example, in a telephone exchange building where the powersupply and maintenance service already is available and that theattendants switching and recording station may be located forconvenience in a difierent building, perhaps several miles removed fromthe telephone exchange. Thus, all the repeater equipment of the mainstation shown in the drawings to the left of the hub circuits H, H-l andI-I-Z is located in the telephone exchange building and the attendantsequipment shown to the right of the hub circuits in the various figuresis located in the distant switching station. For this reason, the relaycontrol circuits have been designed in such a manner that the number ofwires for connecting the attendants station with the repeater stationwill be as small as reasonably possible.

In general, the arrangement is such that any one of the substations maycall the attendant as by operating the calling bell CB shown in Fig. 2and by lighting an indicator lamp, such as IA, IB, CIC, representing theline, or the lines with which the calling station is grouped. Theattendant then operates a key for associating the line with an idle hubcircuit and an attendants recorder. Upon reading the request of thecalling station, the attendant operates keys associated with the calledline or lines and also associated with the selected link circuit,thereby interconnecting the calling and the called lines with theattendants recorder. Two-way communication may then be carried on in anymanner between the lines and will be recorded at both the attendantsstation and headquarters. At the cessation of the conversation, thelines are disconnected from the hub by the attendant restoring theoperated keys, which are of the locking type.

When headquarters wishes to broadcast to all the stations, a special keyis operated at headquarters for sending a seize-all signal to thebroadcasting control circuit B00 in Fig. thereby operating switch CS acorresponding number of steps to establish a connection and operaterelays whereby all stations are cut through to the main or broadcasting1111b including such stations as may a a y be in intercommunication overany of the other link or hub circuits. At the end of a broadcast, thepreviously established interconnections will be reestablished by therestoration of switchCS to normal position. I

The system is based on the hub type of repeater system disclosed in theKinkead-Locke application already referred to. In that system, each lineincoming to the repeater station has permanently assigned to it aninterconnecting repeater which has a line side and a local side. Thelocal side of the repeaters are directly interconnected by the one-wirehub circuit represented in the present instance by any of the linkcircuits H, HI, H2, etc. The hub circuit connects the armature of thereceiving relay in the various repeaters in multiple, and. the windingof the sending relay of each repeater is normally connected to the hubin the marking position of the receiving relay so that it at any timewill be in condition to receive signals from the hub for transmissioninto its associated line circuit. A great number of sending relays maythus be simultaneously operated in multiple over the hub circuit. Thereceiving relay of any one of the repeaters will respond to incomingsignals from its line circuit and in spacing position will place aground on the hub circuit for operation of the sending relays of all theother repeaters. It is evident that in view of the multiple con nectionof such a large number of receiving relays to the hub circuit, thecurrent load on the contacts of any one of the receiving relays will beheavy; for this reason the winding on the sending relay is connectedinto a bridge circuit, so that current reversals may be obtained with acomparatively small current passing over the marking contact of thereceiving relay. It is also desirable to protect the contacts of thereceiving relay by condensers and inductive loading. An arrangement ofbridgecircuit and contact protection suitable for this purpose isdisclosed in an application Serial No. 32,858, filed by G. C. Cummingson July 24, 1935.

In the following, a description will be given of the operation of thesystem illustrated in the drawings under different conditions in orderthat the features and advantages of the invention may be more fullyunderstood.

It will first be assumed that the system is in idle condition with allrepeater relays, control relays and keys in the positions shown in thedrawings, and also that the teletypewriter motors at all substations areat rest;

One of the stations SA now opens the line circuit LA, Fig. 1, by meansof the usual break key and thus sends a break signalto the repeater RA.The line circuit LA is normally under current from positive potential atmarking cont-act of the sending relay S through the upper operatingWinding of receiving relay R, over the line conductors and the threestations SA in series to negative potential at the repeater; relay R isheld in marking position by this current. Current flows also through thelower or biasing winding of relay R from the marking potential at relayS through the balancing network. H to ground, which current tends tomove the armature to spacing but, being of only half the strength of theline current, is unable to do so. When now the break signal arrives, the

line winding becomes currentless and relay R is.

operated to spacing by its biasing winding. The spacing contact of relayR is connected over conductor 22l to ground at the back contacts ofrelay EE in Fig.2. This ground will now be extended over the spacingcontact of relay R, spoke conductor SPA, over back contacts or relaysD2, Dland B, through winding of relay C to battery, these relays beingincluded in the relay control circuit'RCCA associated with re peater RAand line LA.

Relay C, on operating, connects a locking ground over the back contactof relay B to its own winding, connects ground to the marking contact ofrelay R for a purpose which will be described below, and at itsright-hand front contact closes a shunt path for resistance I28. Theseries circuit including this shunt path may be traced from batteryatthe back-contact of relay E, Fig. 2, through winding of relay AA,conductor 225, front contact of relay C, through winding of relay A,resistance I35, indicator lamp-IA, and normally closed contacts of keysKA2, KA-l, and KA to ground. Resistance I28 is connected over conductor226 tobattery at relay E in Fig. 2: and normally supplies enough currentthrough relay A to operate that relay but not enough current to lightthe lamp IA; relay AA, Fig. 2, has a low resistance winding so that, dueto the shunt path for resistance I28 completed by relay '0, the currentin the series circuit is now suf+ ficient to light the lamp and thusindicate to the attendant that line LA is calling. Relay AA, onoperating, applies ringing current to the calling bell CB, Fig. 2, foran audible signal.

The attendants set AP, Fig. 3, is connected to the hub circuit H throughthe plug and jack J, and the motor of the set is normally running. Thesignaling circuit for the set AP may be traced from negative potentialin hub repeater HR, conductor 352, alternate contact and sleeve of jackJ, through the plug and the set, over the tip of jack J, two sets ofnormally closed contacts in multiple of attendants key AK, conductor 35Lupper line winding of relay R in hub repeater HR to positive potentialat-the marking contact of sending relay S. Relay R is operated tomarking in this circuit and thereby connects the bridge circuit forsending relay S, including battery 3l5, over its marking contact to thehub conductor H which extends through back contacts in multiple ofrelays .E and EE, Fig. 2, to the link or hub circuit H in Figs. 2, 1 and1-A.

The attendant now operates key KA, Fig. 1, disconnecting ground fromlamp IA, which be: comes extinguished, and releasing relays A .and AA.The bell signal stops and relay A in relay control circuitRCCA inreleasing operates relay B which at its back contact opens the lookingcircuit for relay C and at its front contacts cuts the hub circuitHthrough to the armature of relay R in repeater RA. Relay C, uponreleasing, disconnects ground from the marking contact of relay Randopens the by-pass for resistance I28. l l

The break signal from station SA will have been discontinued at thistime so that relay R will be in marking position when the hub circuit iscut through, thereby connecting the bridge circuit of sending relay Sfor operation by the attendants set AP over the spoke conductor SPA andhub H. When the attendant now sends an answering signal by opening andclosing the line circuit 35!, 352, Fig. 3, relay R in repeater HR willrespond in the same manner as described for relay R in repeater RA,Fig. 1. During a spacing signal, repeater HR will place a ground overthe marking contact of relay R upon the hub H which will pass over themarking contact of relay R in repeater RA, Fig. 1 to operate relayfi tospacing; relay S then applies negat v sweat ot n l re h the ine nding ofrelay R over the line circuit LA and'stations SA to negative potential.at the repeater RA. The line .current becomes 'zero .andoperates allthe stations SA to spacing. The current through the .biasing winding ofrelay R :in repeater RA now being'reversed, this relay will remain inmarking position. When. repeater HR, Fig. 3 receives a :marking impulsefrom the attendants set AP, relay R disconnects ground from the hubandconnects the :hub to,thexbridge circuit of .relay S in repeater HR; thedisconnection of ground from the hub H removes ground from relay S inrepeater RA, Fig.1, which consequently returns to marking "position,applying markingpotential to the line circuit and retaining relay -R inmarking position.

The .calling station SA' may now state its requirements which may be forconnection with the stations on the line circuits LB. The attendant thenoperates key KB, Fig. 1, thereby disconnecting ground from the seriescircuit through relay A and resistance 128 in the relay control circuitRCC-B over conductor 226, .to battery at relay E, Fig. 2, causing relayA to release and operating relay B. The hub H thus will be cut throughover the spoke conductor SP3 to the armatures in multipleof thereceiving relays R in the individual line repeaters RB-l, RB--2, andRB3. Thus, the hub is extended over the marking contacts of thesereceiving relays to the bridge circuit of their corresponding sendingrelays and communication may now take place between the station's SA andthe stations SB over the hub H. Whenever ground is applied over thespacing contact of one of the receiving relays R to the hub, all theremaining sending relays connected to the hub will be operated tospacing to apply spacing potential to their individual line circuits;when ground is again removed, the sending relays return to markingposition to apply marking potential to their individual lines.

If the request from station SA had also included for example the linecircuit LC, the attendant would then also operate the key KC in the keycircuit KCC, Fig. 1A, thereby also cutting the hub H through to repeaterRC. Any and all of the stations SA, SB and SC, would thus be in two-waycommunication-over the common link'or hub H. l r I All the signalsplaced upon the hub H will pass through the hub repeater HR, Fig. 3, andwill be recorded on the attendants set AP. The sig-' nals will also beimpressed upon the sending relay SR, which constitutes a one-wayrepeater. Relay SR operates in thesame manner as the sending relaysin'the other repeaters and retransmits signals in any desirablemannertoa recording equipment BCR at the broadcasting station orheadquarters 'for recording of all messages over the hub H.

When observing that the conversation-between line circuit LAand linecircuit 'LB has come to an end, the attendant restores the keys -KA andKB, thereby releasing relays B and again-operating relays A in the relaycontrol circuits RCC-A and RCC-B without lighting the lamps. The releaseof relays Bdisconnects the line repeaters from the hub H, and completesthe circuit to relay C, which thus will be ready for the next call.Provision may be made for the attendantto send a special stop signal, ina well-known manner, thereby stopping all the --motors at stations SAand SB, before restoring'the keys KA and Assuming that the connectionover hub "H rbetween line circuit LA and line circuit LB is stillmaintained and that now a .call is originated at station SC, Fig. 1-A,by a break signal, the line circuit may be traced as follows: Fromnegative .potential .at the relay control circuit RCC-C over the line LC.and station SC, left-hand winding and front contact of relay C, linewinding of relay R, to positive potential at the marking contact ofsending relay S in repeater RC. This line circuit will now be opened,causing relay C to release and relay R to operate to spacing. Relay C,in releasing, closes a shunt path about resistance I28, as previouslydescribed, thereby operating relay AA, Fig. 2, and causing the bell CBto ring and also lighting the lamp CIC in the key circuit KC--C.

The attendants set API is associated with the second hub H-l through theplug and jack J--| and hub repeater H-IR. 'I'he attendant will thenoperate the key KC-l in the key circuit KC-C, thereby extinguishing thelamp 010 and releasing relay ;A. Relay A operates relay B, which, on itsleft-hand front contact connects the line circuit'LC through to the linewinding of relayR in repeater RC. Relay 1B also operates relay Cfor-cutting the first hub circuit H through to spoke conductor 'SPCleading to the armature of receivingrelay R in repeater RC. By theoperationof key KC|, the operator also connects ground through thewinding of relay D--l to battery over conductor 226 and back contact ofrelay E, Fig. 2. The operation of relay D-| disconnects the repeater RCfrom the contact of relay B and the first hub before relay B operatesand switches the repeater RC into connection with the second .hub H-land thereby connects the line LC into communication with the attendantsprinter set AP-l.

Complying with the request from station SC, the attendant may .nowconnect any other line circuit to the second hub by operation of theproper key. Thus, the second hub may be connected through relay controlcircuit RCCD to the repeater RD for communication with the stations SD,Fig. IA. The repeater RD has its local side arranged in the same manneras, for example, repeater RA and the relay control circuit RCC-D may .be.equipped in accordance with the detailed showing forthe relay controlcircuit RCCC,'Fig'. '1A, or ,RCCA, Fig. 1. The .repeater RD hasits lineside connected over a line conductorjLD through .the line windings inseries or polarrelays-R-J .and R to contacts of sending relay S,ofrepeater RD- l. The marking potential applied to this circuit atrepeater RD is positive and themarking potential applied. by repeaterRD-l is negative, causing a normal line current to flow vfor operationof the line relays to marking. When thesending relay in either repeaterRD or RDl is operated-to spacing the line circuit just described will beconnectedto the same potential at both ends, rendering it currentlessand. causing the .distant receiving relay to operate to spacing. Thus,when signals are transmitted from the hub H-l through sending relay S inrepeater RD relay S will retransmit the signals .overlineyIiD andoperate relay R-| and R accordingly.

The receiving relays R of the repeater group comprising repeatersRDI,RD2, RD-3, etc., have their=armatures directly interconnected bya-local hubcircuit HD, which in the marking position or the-relays R isconnected to the sending relays of 'the "repeaters. When relay R inre..-

peater RDI responds to spacing impulses from the line circuit LD it willapply ground to the local hub HD and thus operate all the other sendingrelays connected to the hub. Each sending relay then retransmitscorresponding impulses over their associated line circuits LD2, LD-3,etc., for operation of the various substations SD. Spacing impulsestransmitted by any of the stations SD will operate the correspondingreceiving relay to place ground on the hub circuit 1-11) for operationof all the other S relays, including the S relay in repeater RD-l, whichconsequently retransmits the signals through relays R and R-l, withoutaffecting these relays, and over the line circuit LD, operating relay Rin repeater RD. From there, the impulses are repeated over the hub I-DIinto repeater RC and line circuit LC and over the one-way repeater SRI,Fig. 2, to the recorder BCR at headquarters, as well as over hubrepeater HIR to the attendants printer set AP-l, Fig. 3.

It will now be assumed that the two sets of connections established overthe main hub H and the second hub Hl, in accordance with the descriptiongiven above, are maintained and that a broadcast call arrives fromheadquarters to the broadcast control circuit 1300, Fig. 2. For thispurpose, the transmitting equipment BCT at headquarters is operated by aspecial call key to send five long spacing impulses over the line BL,thereby operating receiving relays Rd and Rb.

Relay Ra. in operating sends ground impulses over its spacing contact,resistance 233, conductor 232, two sets of contacts in multiple of theat-' tendants key ABK, Fig. 3, the tip side of jack BJ, to attendantsbroadcast receiving printer ABP, over to sleeve side of jack BJ, to.negative potential, causing the attendants set ABP to be started up inany Well-known manner. With the motor of the set running, relay 36! willbe operated in the power supply circuit, thereby removing the groundfrom conductor 362 connected through contact on key ABK to conductor23!.

Relay Rb in responding to the spacing impulses from headquartersinterrupts at its marking contact the ground applied to slow releasingrelay G, which is slow enough to make the relay nonresponsive toordinary telegraph impulses and yet respond to the special callimpulses. Relay G, consequently, will release five times, each timeapplying ground to rotary magnet ROT of the counting switch CS which,therefore, makes five steps and stops on the segment connected to theconductor 239. As soon as switch CS leaves its normal position, acircuit will be closed over the off-normal contacts from the spacingcontact of relay Rb to slow release relay F, which consequent ly willoperate and will remain operated during the comparatively shortintervals between the long call signals until the switch reaches itsfifth position and relay Rb remains in marking position long enough topermit relay F to release. In this manner the ground applied by theswitch-arm to the first four segments of the switch is prevented fromoperating the release magnet Rel.

The switch CS in its fifth position applied ground over conductor 230 tooperate relays E and EE. Relay EE disconnects ground from conductor 22i, thereby removing ground from the marking contacts of all the linecircuit repeaters and converting them into one-way repeaters during thebroadcasting period. In case this feature is not desired, the switchinglatch 220, Fig. 2, may be swung into position to permanently connectground to conductor 22I, thereby permitting of two-way communicationalso during the broadcasting period as for conference purposes. Relay E,in operating, removes battery from conductor 226, thereby releasingrelays D-J in relay control circuit RCCC and a corresponding relay inthe relay control circuit RCCD and any other D relay which may have beenoperated for connecting the hubs through to the line repeaters. Theremoval of battery from conductor'226 by relay E also causes the releaseof all A relays in the system which, in turn, causes the operation ofall B relays which have not already been operated. In this manner, themain hub H will be out through to all outgoing repeaters forcommunication of the broadcast to all substations.

When now the broadcasting station transmits ordinary signaling impulsesslow release relay G will remain unafiected, and relay F will operate onthe arrival of a first spacing signal and will remain energized duringthe transmission of ordinary telegraph signals. Relay Ra, Fig. 2, inresponding to the signal impulse will repeat the impulses over itsspacing contacts, resistance 233, conductor 232, key ABK, Fig. 3, intothe attendants broadcast printer ABP for recording of the broadcast.Relay Ra over its spacing contact repeats the signals over the frontcontacts in parallel of relays E and EE into the main hub H.

At the end of the broadcast, a special -stop signal will be transmittedover the line circuit BL which will be applied to the hub H and causeall printer motors to stop including the motor for the attendantsprinter ABP andpreleasing relay 3E6 in the power supply circuit for themotor of this printer. After the reception of this signal, relay Rb willremain in marking position, thereby causing relay F to release after aninterval. Ground will therefore be applied from the back contact ofrelay 36L Fig. 3 over conductors 362 and 23!, contact of relay F, oil?-normal contact of switch CS to the release magnet Rel which will causethe switch-arm OS to return to normal; the release circuit is alsomaintained in positions I, 2, 3, 4 of the switch by ground from theswitch-arm.

Relays E and EE now release to disconnect the broadcast line from themain hub and battery is again connected to conductor 226 for operationof all A relays for which the associated key circuit is in normalposition. In the assumed case, relays A in the relay control circuitsRCCA and. RCCB will not be operated because the keys KA and KB have beenoperated to remove ground from the corresponding series circuits. Therelays B in these two control circuits consequently remain operated andthe main hub H remains in connection with the line circuits LA and LB.Thus, if it should be desired to continue the communication betweenthese line circuits, any one of the stations SA and SB may transmit astarting impulse for starting the motors of all the other stations SA,SB over the main hub circuit for continuation of the communication.

, Similarly the A relays in relay control circuits- RCC-C and RCC-D willremain unoperated and. relay D-I in circuit RCC-C and the correspond ingD relay in the circuit ECG-13 will again be operated by battery overconductor 226 from mlay E, Fig. 2, thereby reestablishing theconnecprinter set AP--l connected to the second hub HI and the attendantwill restore the key KC-I, Fig. 1A, and the corresponding key in the keycircuit KCD.

A spare printer set ASP is provided which may be substituted for any oneof the other sets by operation or the corresponding keys ABK, AK, AK-I,and AK-2 which will insert the spare set serially in the line circuitthrough the respective jacks.

Special provision has been made to prevent a conversation from takingplace between two stations at any point in the entire system'without theattendants knowledge and without being recorded at the repeater stationand headquarters.

Thus, when one of the stations SA transmits a break signal, the otherstations SA on the same line circuit would be started up and it would bepossible for these stations to exchange messages before the attendanthad connected the line circuit to a hub associated with a recorder. Inorder to prevent this, a ground is immediately placed on the markingcontact of the receiving relay of repeater RA. by the operation of therelay C in the relay controlcircuit RCCA; this ground operates the Srelay of repeater RA to spacing, thereby rendering the line currentlessand preventing communication between the stations. As soon as the Brelay has been operated by the operation of one of the keys in the keycircuit KCA, the C relay is released and the ground is removed from themarking contact of relay R and relay S returns to markmg.

Depending upon the motor control system used at the teletypewriterstations, it will be possible by the grounding arrangement justdescribed to not only prevent exchange of signals between the stationswithout monitoring but also to prevent the motors of the teletypewriterequipment from starting. Thus with a teletypewriter equipment such asdisclosed in Patent 1,904,164 to Morton et al. on April 18, 1933, at thesubstations, the motor of each output included in a particular line orloop may be started by first opening at any point the normally closedloop and then again closing the loop. The motor will then continue torun during the subsequent O signaling until two specially assignedsignals are impressed upon the loop; in the present instant the twospecial signals are twoshift signals in immediate succession.

Thus when the calling station in sending the break signal first opensthe line, the contact operating mechanism in each printer on line LAtakes its first step and relay C operates the sending relay S inrepeater RA to spacing. Both line conductors will consequently becharged to spacing potential when at the end of the break signal theline is again closed, and the contact operating mechanism in theprinters will not take its second step and start the motor until the.attendant has associated the line with a hub or link, thereby releasingrelay C and permitting relay S of repeater RA to return to markingposition. The motors at station SA and at the attendants set AP may nowbe stopped at any time by two successive shift signals from any of thesestations or from any other set connected to the hub.

In the case of the. line circuits LB-l, LB-2, and 13-3,. communicationmight be. established between. these line circuits over the r pe tersRB'.I, RB--'2, and RB-3 before the hub circuit HB was connected throughto one of the link circuits by the attendant. In this case, the C relaywill operate relay CC which, in turn, operates to place ground on themarking contacts of the R relays in repeaters RBI, RB-Z, and REP-3thereby operating the sending relays to spacing and preventingcommunication between the stations SB until a key in the key circuitKC-B has been operated; thereupon relay C and relay CC will release toremove the ground and recondition the repeaters for two-waycommunication.

A similar arrangement may be provided for repeater RC, Fig. lA.

For the remote groups of stations, such as the group of stations SD,Fig. lA, which may have their line circuits interconnected through aplurality of repeaters such as RD2 and RD-3, over a local hub Hi), thegrounding of the marking contacts of the various receiving relays isdone by relay CC in the group control circuit GCC. When one of thestations SD calls by sending a long break signal, the signal will berepeated by repeater RD-I over line LD to the repeater RD at the mainstation. In this circuit, the receiving relay R of repeater RD-l and itsassociated relay Rl will remain in marking position whereas receivingrelay R in repeater RD will be operated to spacing and in turn willoperate relay C in the relay control circuit RCC--D. As described forthe relay control circuit RCC-A, the C relay in the relay controlcircuit RC-D will place a ground on the marking contact of relay R inrepeater RD operating the sending relays of this repeater to spacing.The line ID will be connected to negative potential at repeater RD andto positive potential at repeater RDI and a current will flow to operaterelay R in repeater RD-l and relay R-l to spacing against the breaksignal from the calling line. Relay R-l will remove ground from thenormally operated relay GG, and whereas this relay is sufiiciently slowreleasing to be non-responsive to ordinary signal impulse combinations,it will now have time enough to release and cause the operation to relayCC to prevent communication between the stations SD before the end ofthe break signal from the calling station.

When the attendant at the main repeater station responds by operatingone of the keys in the key circuit KC-D, the C relay in the relaycontrol circuit ROG-D will be released and the spacing condition will beremoved from the line circuit LD. Relay R of repeater RD-l and relay R-Ithen operate to marking, causing relay GG to operate and relay CC torelease, placing the line circuits RD-Z and RD3 in condition for two-Waycommunication, at which time such communication will be recorded at themain repeater station and at headquarters.

If desired, the system may be arranged in such a way that upon requestfrom any one of the substations, the attendant, by operating thebroadcasting key BK, Fig.2 will arrange the system for broadcast fromthe calling station to all the other stations or for conference betweenall the stations. For this purpose, the broadcasting key will operaterelays E and EE, Fig. 2, in the same manner as does the switch CS,thereby removing the battery from conductor 226 and connecting allrepeater circuits to the main hub.

The key circuit KCC' Fig. 1A may b an ranged exactly as the circuitsKC--A and KC--B. A modified circuit has however been shown in thedrawings which has certain advantages. Thus in instances, such as thepresent, where the key circuits KC are connected over comparatively longwires to the relay control circuit RCC, the lamps I may be subject todischarges due to atmospheric disturbances when directly connectedbetween these conductors and ground, as shown in the key circuits KC--Aand KCB. This is avoided in key circuit KCC by substituting for thecalling lamp a relay CRC in the series circuit I30; relay CRC operatesunder the same conditions as cause the calling lamps IA and IE to lightup, and it closes an auxiliary circuit for the calling lamp CIC.

The key circuit KCC also includes a test lamp TIC which is normallyextinguished by the normally operated test relay TRC, also included inthe series circuit I 30. Relay TRC is released when any one of the keysKC is operated and lamp TIC is lighted and in this case serves as a busylamp. However, relay TRC would also release if, during idle condition ofthe line LC and its associated equipment, an accidental open shouldoccur in the series circuit I30. Thus the lighting of lamp TIC when noneof the keys KC is operated would indicate to the attendant that line LCis unable to call.

What is claimed is:

l. A telegraph switching system comprising a line circuit, call relaymeans responsive to calls on said line circuit, control relay means forcutting through said line circuit for communication with a signalingcircuit, and a series circuit incircuit to make said device indicatingwithout operating said control relay means.

2. A telegraph switching system, in accordance with claim 1, whichfurther comprises remote control switching means having contacts foroperation of said control relay means by opening said series circuit.

3. A telegraph switching system comprising a line circuit, call relaymeans having a winding normally energized over said line circuit whensaid line is closed, control relay means for cutting through said linecircuit for communication with a signaling circuit, call indicatingmeans responsive to release of said call relay means, manual switchingmeans for simultaneous control of said control relay means and saidindicating device, said control relay means having contact means forexcluding said winding from said line circuit dur.

ing communication.

4.. A telegraph switching system comprising a plurality of line circuitseach having a terminal circuit at a switching station, a local linkcircuit at said station, each of said terminal circuits including callrelay means having a winding normally included in the associated linecircuit for control of call indicating means, control relay meansoperative to connect said terminal circuit to said link circuit forcommunication through another of said terminal circuits and to excludesaid winding from said line circuit, and manual switching means foroperation of said control relay means.

5. A telegraph switching systemin' accordance with claim 4, furthercomprising remote control switching means common to said plurality ofterminal circuits and responsive to calls over a special line circuitfor operation of said control relay means in all of said terminalcircuits.

6. A telegraph switching system comp-rising a plurality of line circuitseach having a terminal circuit at a switching station for two-way communication, a local link circuit at said station, an attendants circuitconnected to said link circuit for receiving calls over said linecircuits, control relay means included in each terminal circuit forcutting the associated line circuit through to said link circuit, andmanual switching means associated with each of said terminal circuitsfor operation of said control relay means to cut through to said linkcircuit any number of said plurality of line circuits for two-waycommunication between them.

7. A telegraph switching system comprising a plurality of line circuitseach having a terminal circuit at a switching station for two-waysignaling, a first local'link circuit at said station, a second locallink circuit at said station, control relay means included in each ofsaid terminal circuits for cutting the associated line circuit throughto said first link circuit, first manual" switching means associatedwith each of said terminal circuits for operation of said control relaymeans to cut through any number of said line circuits to'said first linkcircuit for two-way communication between them, switching relay meansincluded in each of said terminal circuits for switching the associatedline circuit from said control relay means to said second link circuit,and second manual switching means associated with each of said terminalcircuits for operation of said switch relay means to cut through anynumber of said line circuits to said second link circuit for two-waycommunication between them.

8. A telegraph switching system comprising a plurality of line circuitseach having a terminal circuit at a switching station for two-waysignaling, a plurality of local link circuits at said station forinterconnection of said line circuits, each of said terminal circuitsincluding a locking key and control relay means operable by said key foreach of said link circuits for connecting the associated line circuit toany one of said link circuits, common switching means operable to aselective position for control of said control relay means to switch theconnection of all line circuits set up by said keys to one of said linkcircuits from any other link circuit.

9. A telegraph switching system, in accordance with claim 8, inwhichsaid control relay means are connected for control by said locking keysand by said common switching means so that a subsequent operation ofsaid switching means to another position will restore all theconnections of line circuits to the diiferent link circuits inaccordance with the setting of said keys.

10. A telegraph switching system comprising a plurality of line circuitseach having a terminal;

through to the first of said link circuits, other control relay meansfor switching the line circuit to another of said link circuits, callrelay means having a winding included in said line circuit during idlecondition, call indicating means and a plurality of locking. keysincluded in a local call circuit, said call relay means having contactmeans for operating said call indicating means, said locking keys eachhaving contacts to disconnect said indicating means and to operate acorresponding one of said control relay means, and said first controlrelay means being connected to be operated by all of said keys and.having contacts to exclude said winding from the: signaling path of saidline circuit.

11. A telegraph switching system, in accordance with claim 10, furthercomprising a special line circuit having a terminal circuit at saidswitching station including common relay means and selective switchingmeans operable to a predetermined condition in response to a signal oversaid special line to operate said common relay means, said common relaymeans having contacts for controlling said other control relay means todisconnect line circuits from thecorresponding other link circuits andfor controlling. said first control relay means to cut through all ofsaid plurality of line circuits to the said first link circuit. 7

12. A telegraph switching system comprising a. plurality of linecircuits and a special line circuit and interconnecting circuit means ata switching station, each of said line circuitshaving terminal equipmentat said switching sta-. tion, the terminal equipment for each ofsaid.line circuits comprising call. relay means responsive to calls on saidline circuit, control relay means for conditioning said line circuit forcommunication with said circuit means, and a series circuit including awinding of said control relay means, resistance means, a call indicatingdevice, and. manual switching means for operation of said. control relaymeans by opening of said series circuit, the winding of said controlrelay means being normally energized when the associated line circuit isidle, said call relay means having contacts for reducing the resistancein said series circuit in response to a call to operate said in.-dicating device without deenergizing said' winding, and said seriescircuit being connected to a common current source, and the terminalequipment for said special line circuit comprising, remote controlcontact means for operation of said plurality of control relay means inresponse to a broadcast call on said special line circuit bydisconnecting said plurality of series circuits from said common currentsource when in a selected position and for connecting said source tosaid series circuits when subsequently moved to another position by adisconnect signal on said special line circuit. I

13. A telegraph switching systemcomprising a plurality of line circuitsterminating at a switching station, a plurality of link circuits,manually controlled relay means for each connection point between said.line circuits and said link circuits for setting up of a plurality oftwo-way connections between said line circuits, characterized in thisthat said system further includes switching means for automatic controlof said relay means to connect all of said line circuits to. one of saidlink circuits for two-way communication between them in one position ofsaid switching means and for restoring all manually set up connectionsbetween said line circuits and said link apmcae.

circuits when subsequently operated to another position- 14. A pluralityof telegraph stations, a repeater station, a linev circuitinterconnecting said stations, said repeater station including sendingrelay means for normally applying current condition and alternatelyapplying no-current condition to said line circuit, said repeaterstation also including receiving relay means responsive to currentimpulses over said line circuit under said current condition, controlrelay means connected' for operation by said. receiving relay means inresponse to an open ofv said line circuit for operation of said sendingrelay means to apply the no-current condition to said line circuit.

15. A plurality of line circuits including telegraphv stations, aplurality of repeater circuits for interconnection of said line circuitsand including sending relay means for normally applying currentcondition and alternately applying no-current' condition to said. linecircuits, receiving relay means responsive to current impulses over saidline circuit under said current condition, and control relay meansconnected for operation by said receiving relay means in response to anopen of said line circuits for operation of said sending relay means toapply the no-current condition simultaneously to all of said linecircuits.

16. A plurality of line circuits including telegraph stations, aplurality of repeater circuits for interconnection of said line circuitsand each including sending relay means for normally applying currentcondition and alternately applying no-current condition to theassociated line circuit, and receiving relay means responsive to currentimpulses over said associated line circuit under said current condition,control relay means, at one of said stations responsive to theno-current condition on the associated line circuit to apply reversedcurrent condition to said line cirwit to operate said receiving relaymeans of the associated repeater circuit, and slow-acting common relaymeans responsive to the operation of said receiving relay means tooperate the sending relay means of the other of said repeater circuitsto apply no -current condition to the other of said line circuits.

17. A line circuit, a plurality of telegraph stations on said linecircuit each including recording mechanism arranged for automaticstarting by an interruption and a subsequent restoration of the normalcurrent condition on said line circuit, repeating means for terminationof said line circult and normally applying current condition to said.line circuit, control relay means connected to said repeating means foroperation in response to an. open of said line circuit at one of saidstations to in turn operate said repeating means to apply no -currentcondition to said line circuit to prevent starting of said plurality ofrecording mechanisms.

18. The combination, in accordance with claim 17, further comprisingrelay means and manually controlled contact means for restoring saidcontrol means and said repeater means to apply current condition to saidline circuit and start said plurality of recording mechanisms.

FULLERTON S. KINKEAD. GEORGE A. LOCKE.

